Speaking at a meeting of the regional development committee, Sara Venning also hit out at Stormont's inability to agree long-term budgets.

"Our delivery model constrains us as an organisation - we could do more," she said. "There is not a medium-term financial settlement in place for NI Water. We are a very asset-intensive industry, and asset-intensive businesses need to plan for the long-term.

"Our comparators in England and Wales get a five-year programme of work. We live year-to-year in terms of budgeting."

NI Water representatives appeared before the committee in December to talk about their annual accounts and report.

The Assembly's public finance scrutiny unit examined those documents and produced a report that questioned Ms Venning's £145,000-£150,000 pay packet, an increase in loans and debts, a drop in profits and a low number of female workers.

NI Water's debt has increased from £19m to £23m, its loans have increased by £33m and its profits are down by £50m since 2013-14.

However, Ms Venning said the past year had been broadly successful for the organisation.

"There was a strong performance both financially and also from a service point of view," she added. "The one area of concern that is highlighted by the external auditors is the lack of funding for the next business period - that was flagged in the annual reports as a concern.

"The accounts demonstrated a strong performance by the company, but there were some areas of challenge for us in the year 2014/15. The first was that of the industrial action of this time last year, which impacted adversely on our score for customer service.

"That was disappointing for all of us in the company because we have been very consistent in our message that we are an organisation that exists to serve customers.

"We have on many occasions indicated that our company's constitution, as being Government-owned, hampers our ability to deliver for customers, and that is becoming more apparent as we enter into this environment of public sector constraints."

Ms Venning also insisted that "delivering more for less is something NI Water has been doing for some time".

"These accounts demonstrate that during the year 2014/15 we reduced our running costs by 4%," she said.

"We have moved from being 49% behind our comparator companies in England and Wales.

"We have closed that gap by two-thirds, and we are now recognised as being 13% behind those companies. That is a real shift, a real improvement."

Meanwhile, committee deputy chair and Sinn Fein MLA Sean Lynch condemned the leaking of the report to yesterday's edition of the Belfast Telegraph as "disappointing" and "irresponsible".

He said it was not classified as a secret document, but that there was an understanding that it should not be given to anyone outside the committee.